Waves in a plasma

This post follows from a comment I had yesterday from Robert McCormick on the www.sciblogs.co.nz version of PhysicsStop. (Unfortunately the mapping of PhysicsStop onto the sciblogs website doesn't combine the comments - so if you read my blog through The University of Waikato website you won't have got his comment, so I attach the link below)

http://sciblogs.co.nz/physics-stop/2009/12/03/rainbows/#comments 

Plasmas provide a wonderful medium for waves. A plasma, in simple terms, is a gas (often very high temperature) consisting of charged particles (e.g. electrons and positively-charged molecules). As well as bouncing around like your normal gas molecules will do, the particles in the plasma feel the electric and magnetic fields that each other create, leading to a great array of possible ways for waves to travel. So plasmas can carry sound waves, electromagnetic waves and bizarre combinations of  both.

I studied a little plasma theory while I was an undergraduate and found in fascinating. I can't say I've had much to do with plasmas since, but the theoretical techniques I learnt about for analyzing waves in plasmas have proved really useful for other physical situations, such as waves of neuronal activity in the brain. It's an example of how the same underlying phenomena can manifest themselves in very different physical systems. And it's an example of how to answer the undergraduate student how says 'Why am I studying this stuff - I'm never going to use it'.